Remove qualifying lines of text from string including its leading newline or trailing newline, but not both

In the following regex:

EXCLUDE this entire line
include this line
and this as single match
and EXCLUDE this line

I want to return a single match consisting for two lines:

include this line
and this as single match

I want to use EXCLUDE as string identifying that the entire line should not be included.

edit: if I can get just the first match up to the line with "EXCLUDE" (or end of document whichever happens first), that would work too

With pcre you can use \K to fotget what is matched so far, and first match the line containing exclude:

^.*\bEXCLUDE\b.*\K(?:\R(?!.*\bEXCLUDE\b).*)+

Regex demo

If you want to match all lines that do not contain exclude, with consecutive lines:

(?:(?:^|\R)(?!.*\bEXCLUDE\b).*)+

Regex demo

Or using a skip fail approach:

^.*\bEXCLUDE\b.*\R(*SKIP)(*F)|.+(?:\R(?!.*\bEXCLUDE\b).*)*

Regex demo